5,345 research outputs found
A Tunable Echelle Imager
We describe and evaluate a new instrument design called a Tunable Echelle
Imager (TEI). In this instrument, the output from an imaging Fabry-Perot
interferometer is cross-dispersed by a grism in one direction and dispersed by
an echelle grating in the perpendicular direction. This forms a mosaic of
different narrow-band images of the same field on a detector. It offers a
distinct wavelength multiplex advantage over a traditional imaging Fabry-Perot
device.
Potential applications of the TEI include spectrophotometric imaging and
OH-suppressed imaging by rejection.Comment: 11 pages, 12 figures, accepted by PAS
The Taurus Tunable Filter Field Galaxy Survey: Sample Selection and Narrowband Number-Counts
Recent evidence suggests a falling volume-averaged star-formation rate (SFR)
over z ~ 1. It is not clear, however, the extent to which the selection of such
samples influences the measurement of this quantity. Using the Taurus Tunable
Filter (TTF) we have obtained an emission-line sample of faint star-forming
galaxies over comparable lookback times: the TTF Field Galaxy Survey. By
selecting through emission-lines, we are screening galaxies through a quantity
that scales directly with star-formation activity for a given choice of initial
mass function. The scanning narrowband technique furnishes a galaxy sample that
differs from traditional broadband-selected surveys in both its volume-limited
nature and selection of galaxies through emission-line flux. Three discrete
wavelength intervals are covered, centered at H-alpha redshifts z = 0.08, 0.24
and 0.39.
Galaxy characteristics are presented and comparisons made with existing
surveys of both broadband and emission-line selection. When the number-counts
of emission-line objects are compared with those expected on the basis of
existing H-alpha surveys, we find an excess of ~ 3 times at the faintest
limits. While these detections are yet to be independently confirmed,
inspection of the stronger subsample of galaxies detected in both the line and
continuum (line-on-continuum subsample; 13 %) is sufficient to support an
excess population. This increase in the emission-line field population implies
higher star-formation densities over z ~ 0.4. However, further study in the
form of multi-object spectroscopic follow-up is necessary to quantify this and
confirm the faintest detections in the sample.Comment: 48 pages, 12 figures. To appear in the Astrophysical Journal. An
abridged version of the Abstract is shown her
Evaluation of pyrrolidine and pyrazolone derivatives as inhibitors of trypanosomal phosphodiesterase B1 (TbrPDEB1)
Author Posting. © The Author(s), 2015. This is the author's version of the work. It is posted here by permission of Elsevier for personal use, not for redistribution. The definitive version was published in Tetrahedron Letters 56 (2015): 2832-2835, doi:10.1016/j.tetlet.2015.04.061.Human African trypanosomiasis (HAT) is a parasitic disease, caused by the protozoan pathogen
Trypanosoma brucei, which affects thousands every year and which is in need of new therapeutics.
Herein we report the synthesis and assessment of a series of pyrrolidine and pyrazolone derivatives of
human phosphodiesterase 4 (hPDE4) inhibitors for the assessment of their activity against the
trypanosomal phosphodiesterase TbrPDEB1. The synthesized compounds showed weak potency against
TbrPDEB1.We acknowledge funding from the National Institutes of Health (R01AI082577)
Optimising background-limited observing during bright-moon phases and twilight
For the majority of optical observing programs, the sky brightness provides
the fundamental limit to signal detection such that the scientific feasibility
is largely dictated by the moon phase. Since most observatories do not have the
resources to build expensive high-resolution or infrared instruments, they are
increasingly at a loss as to how to exploit bright time. We show that, with due
consideration of the field and moon position, it is possible to undertake `dark
time' observing programs under `bright time' conditions. Our recommendations
are particularly appropriate to all-sky survey programs.
In certain instances, there are gains in observing efficiency with the use of
a polariser, which can significantly reduce the moonlight (or twilight)
sky-background flux relative to an extraterrestrial flux. These gains are
possible in background-limited cases because the sky background can be highly
polarised, due to scattering, around ninety degrees away from the moon (or
sun). To take advantage of this, only minor modifications to existing
instruments are needed.Comment: 5 pages, 4 figures, accepted by MNRA
Elementary transitions and magnetic correlations in two-dimensional disordered nanoparticle ensembles
The magnetic relaxation processes in disordered two-dimensional ensembles of
dipole-coupled magnetic nanoparticles are theoretically investigated by
performing numerical simulations. The energy landscape of the system is
explored by determining saddle points, adjacent local minima, energy barriers,
and the associated minimum energy paths (MEPs) as functions of the structural
disorder and particle density. The changes in the magnetic order of the
nanostructure along the MEPs connecting adjacent minima are analyzed from a
local perspective. In particular, we determine the extension of the correlated
region where the directions of the particle magnetic moments vary
significantly. It is shown that with increasing degree of disorder the magnetic
correlation range decreases, i.e., the elementary relaxation processes become
more localized. The distribution of the energy barriers, and their relation to
the changes in the magnetic configurations are quantified. Finally, some
implications for the long-time magnetic relaxation dynamics of nanostructures
are discussed.Comment: 19 pages, 6 figure
Bayes and health care research.
Bayesâ rule shows how one might rationally change oneâs beliefs in the light of evidence. It is the foundation of a statistical method called Bayesianism. In health care research, Bayesianism has its advocates but the dominant statistical method is frequentism.
There are at least two important philosophical differences between these methods. First, Bayesianism takes a subjectivist view of probability (i.e. that probability scores are statements of subjective belief, not objective fact) whilst frequentism takes an objectivist view. Second, Bayesianism is explicitly inductive (i.e. it shows how we may induce views about the world based on partial data from it) whereas frequentism is at least compatible with non-inductive views of scientific method, particularly the critical realism of Popper.
Popper and others detail significant problems with induction. Frequentismâs apparent ability to avoid these, plus its ability to give a seemingly more scientific and objective take on probability, lies behind its philosophical appeal to health care researchers.
However, there are also significant problems with frequentism, particularly its inability to assign probability scores to single events. Popper thus proposed an alternative objectivist view of probability, called propensity theory, which he allies to a theory of corroboration; but this too has significant problems, in particular, it may not successfully avoid induction. If this is so then Bayesianism might be philosophically the strongest of the statistical approaches. The article sets out a number of its philosophical and methodological attractions. Finally, it outlines a way in which critical realism and Bayesianism might work together.
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Synthesis and assessment of catechol diether compounds as inhibitors of trypanosomal phosphodiesterase B1 (TbrPDEB1)
Author Posting. © The Author(s), 2013. This is the author's version of the work. It is posted here by permission of Elsevier B.V. for personal use, not for redistribution. The definitive version was published in Bioorganic & Medicinal Chemistry Letters 23 (2013): 5971-5974, doi:10.1016/j.bmcl.2013.08.057.Human African trypanosomiasis (HAT) is a parasitic neglected tropical disease that affects 10,000 patients each year. Current treatments are sub-optimal, and the disease is fatal if not treated. Herein, we report our continuing efforts to repurpose the human phosphodiesterase 4 (hPDE4) inhibitor piclamilast to target trypanosomal phosphodiesterase TbrPDEB1. We prepared a range of substituted heterocyclic replacements for the 4-amino-3,5-dichloro-pyridine head group of piclamilast, and found that these compounds exhibited weak inhibitory activity of TbrPDEB1.We acknowledge funding from the National Institutes of Health (R01AI082577)
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